Zero degrees? Time for baby's outdoor nap

American parents may think they’ve got the naptime drill down, ensuring that their infant is on her back with no loose covers or pillows, possibly in a sleep sack if it’s chilly. But Nordic parents add one element to the mix: fresh air, even in winter.

The age-old Nordic tradition of allowing infants and toddlers an outside nap in a stroller is making headlines after a recent BBC story highlighted the practice. The optimal outdoor temp is 23 degrees Fahrenheit, according to Marjo Tourula, a research coordinator at the University of Oulu in Finland who wrote her thesis on children sleeping outdoors.

Parents she interviewed said they believed sleeping outside would toughen the child to harsh climates, help them sleep and eat better, and contribute to their overall health, according to the BBC.

“In some studies they found pre-schoolers who spent many hours outside generally — not just for naps — took fewer days off than those who spent most of their time indoors,” pediatrician Margareta Blennow said. “In other studies there wasn’t a difference.”

Of course, the babies are bundled up, often in wool, and many parents put cream on their faces in the coldest weather.